Danielle has taught middle school science and has a doctorate degree in Environmental Health
What is Amylose?
Right now, you've probably got some amylose in your kitchen cupboard, like in that box of cornstarch. As you probably already know, cornstarch is a widely used product that thickens foods. But, did you know that amylose in cornstarch contributes to its thickening property? So what is this secret ingredient? Well, amylose is a linear polymer chain that contains hundreds to thousands of glucose molecules. A polymer is a large molecule that contains many subunits.
Let's take a look at that box of cornstarch. As a starch, 20-25% of its content comes from amylose. But what about the other 75-80% of its makeup? Here, we'll find a different compound called amylopectin, which we'll discuss later on in this lesson. Amylose is water soluble, which contributes to the gelatinous property of starch. In other words, because amylose loves to mingle with water, it can help turn a substance, such as cornstarch, into a thickener.
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If you're wondering what amylose looks like, take a look at the two diagrams here.
Check out all those oxygen atoms, carbon atoms, and CH2OH molecules. Collectively, one subunit of amylose is called a glucose molecule, as shown in the illustration. Each glucose or sugar molecule links to another by way of a glycosidic bond, which is a type of covalent bond. Covalent bonds form when molecules share electrons.
Glycosidic bonds are important because they link several hundred, or even thousand, glucose molecules to form an amylose chain. For example, the coiled amylose chain in the diagram contains more than 500 glucose molecules!
Earlier we identified amylose as a polymer. We also found out that a polymer is a gigantic molecule with many subunits. Keeping what we learned at the beginning of the lesson in mind, why would amylose be a polymer? Well, amylose qualifies as a polymer because it is a gigantic molecule formed from several sugar subunits, called glucose, linked together via glycosidic bonds.
In general, amylose can take on one of three different forms or shapes. For example, amylose can be amorphous in shape, or present as one of two different helical forms. When amorphous in shape, the amylose chain looks like spaghetti and has no specific order to the arrangement of its subunits. In either of the two helical shapes, the glucose subunits intertwine, as shown in the diagram above.
Amylose can be found in both animal-based and plant-based starches, where it provides a great source of energy for the latter. In the food industry, amylose aids in thickening, stabilizing, or even gelling products.
So, how does amylose turn starch into a thickening agent? When starch, which contains amylose and amylopectin, is heated in water, the hydrogen bonds break. When they break, water enters into the starch molecule. Amylose doesn't particularly care for hot water, so it moves out of the starch molecule. This leaves plenty of opportunity for amylopectin to hang out with the hot water. As this hydrogen bonding moment between water and amylopectin continues, the entire starch molecule starts to thicken, just like the ones in your pie fillings!
Let's review. Amylose is a type of polymer found in starch. It is a linear chain composed of hundreds to thousands of glucose molecules. It is a water-soluble substance and makes up 20-25% of starch. Amylose can exist in three different forms, including one amorphous and two helical conformations.
Glycosidic bonds link the glucose subunits together when building an amylose chain. A glycosidic bond is a type of covalent bond. Amylose provides energy storage for plants and helps starch products thicken.
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Amylose: Structure, Formula & Function
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